This invention relates to oil field drilling apparatus and more particularly provides a slip mechanism of the type functioning as an elevator or a spider.
Elevators or spiders are well known for use during the lowering or raising of conduits, such as drill pipe, tubing and casing, into and out of a well bore during drilling operations. The elevator or spider can include slips having teeth which engage the casing so that the casing is not inadvertently released into the well bore.
Such slip mechanisms include primary components which are arranged in several basic configurations. The main structure is the slip bowl or body which is generally an enlarged support structure having an internal tapered bore. Slip elements are disposed within the bore and when allowed to fall under the force of gravity, wedge radially against the casing so as to prevent the casing from slipping downwardly. Typically, known assembly structures do not engage the casing or other conduit in a balanced manner, which can unevenly load and damage the casing or limit the gripping force. Raising of the slip elements generally releases the gripping interaction.
The slip mechanisms typically include a structural arrangement which provides a radial opening through the body to allow lateral motion of the slip mechanism onto, or away from, the casing. One such arrangement utilizes a hinged body whereby the body is composed of two or more sections which are hinged together. Another such arrangement utilizes a unitary body of the so called box type which includes a hingedly attached door.
Exemplary of the hinged body design are mechanisms manufactured by Varco International, Inc. and referred to as slip type "SL" casing elevator/spiders. Such units include a body formed in two halves cooperably joined by large hinge pins. Four slips are positioned about the central bore in oppositely disposed pairs, which can disadvantageously result in an unbalanced loading between the two pairs upon gripping of the casing. Exemplary of the unitary body type are those manufactured by Byron Jackson Tools, Inc. which include a double hinged door. This design appears to use three slips which do not overlap the radial opening in the unitary body and which consequently eccentrically surround the casing both prior to engaging the casing and upon gripping and setting of the slips.
Additional slip type structures are known. For example, U.S. Pat. No. 2,641,816 discloses a pneumatically or hydraulically operated power slip including a fabricated slip lift ring having a single hinge gate. Three slip segments are hinged together by pins and are individually connected to arms which slide along trackways in the ring to engage or disengage the slips from a drill pipe. The slips are lifted and moved radially away from the pipe upon lifting of the ring, and fall into a gripping position under the influence of gravity upon lowering of the ring. The three hingedly connected slip segments may be manually moved together to one side of a tapered area or slip bowl upon disengagement from the pipe.
An automatic drill slip unit is disclosed in U.S. Pat. No. 2,575,649 including two ringlike members rotatably interconnected one inside the other and having throats which are registrable to allow placement about a drill pipe. Three slips are suspended from the inner ring by mechanical links. The inner ring is lowered through lifting of a counterweight such that the slips slide along tapered faces of a slip bowl and engage the drill pipe.
A slip type elevator or spider having a hinged door is disclosed in U.S. Pat. No. 3,149,391 including an assembly of three slip elements which are interconnected through vertical pivot pins. Torsion springs positioned about the pins bias the slip elements toward an open position upon lifting of the elements under the influence of a pivoting arm and yoke whereby camming projections on the rear surface of the slips nest into annular depressions of the elevator body.
Another slip type pipe elevator is disclosed in U.S. Pat. No. 3,342,520 having a one-piece generally circular body and three slips carried by cam follower pins mounted on rollers which, upon rotation of an annular plate by an extending manually gripped handle, rise up a sloping cam surface to lift and disengage the slips. The slips withdraw upwardly and radially outward to allow for positioning of the elevator over the upper end of the pipe.
A power driven slip structure is disclosed in U.S. Pat. No. 3,270,389 wherein three slips are separately supported from a body or ring which is raised and covered or laterally swung into position by a fluid powered mechanism. The ring includes a rotatable slip carrier. The slips can also be hinged to one another through vertical hinge pins. The ring includes a main section and a hinged gate section. The central slip is rigidly connected to a support part extending from the slip carrier having a cam slot which guides radial motion of the slip, and the other slips are mounted to two hanger elements suspended from the rotatable carrier having ball ends to form a universal joint type connection to the slips.
Slips for supporting drill pipe in a bowl are also shown in U.S. Pat. No. 4,332,062 which discloses a bowl made of four sections forming an inverted pyramidal opening and having a slip associated with each of the four sections. The slips are connected to an hydraulically actuated lift ring which simultaneously lowers the four slips into an engaged position against the drill pipe.
Further background on spider and slip type structures is provided in U.S. Pat. Nos. 2,063,378; 2,156,384 and 3,846,877.
While many of the discussed structures will operate to perform their intended purposes, improvement can be made. Certain of the structures, for example, require a complex or awkward sequence to properly position and operate. Others in practice unevenly load the pipe, casing or other type of conduit, causing excessive localized stress and wear. Other deficiencies exist. It is therefore desirable to provide a slip mechanism, operable as an elevator or spider, which alleviates prior deficiencies. Such mechanism should preferably be highly reliable, relatively simple to operate, and should alleviate undue stresses imposed upon the conduit being supported, particularly where the conduit is relatively thin walled casing. Such mechanism should provide balanced engagement of a conduit.